The present invention generally relates to the optical field, namely to optic films. More particularly, the present invention relates to optic films used in liquid crystal device (LCD) displays and backlight devices for passing of light, where light falls on one side of a film, and for reflecting of light, where light falls on another side of a film.
The light of a backlight device may not used efficiently. For example, the light of a lamp is reflected partly from the surrounding surfaces and returning to the lamp, causing the lamp blinking or other unwanted effects. It is estimated that only 5 percent of the backlight device radiation reaches an observer because of polarization and a large number of layers in a LCD of the pass-through type. An increase of brightness may be achieved by increasing the lamp power or by using the additional sources of light. This method results in an increase of energy consumption (it is undesirable for portable devices), an increase in cost of the display device and a decreasing of the device's reliability. Thus, a compromise in display design is often sought, sacrificing one group of the LCD parameters for another group's benefit. One of the methods to increase the efficiency of the LCD, includes the development of a special optical construction of backlight device using optical antireflection films.
Optical antireflection films (see U.S. Pat. No. 5,917,664 [1], for example) include a set of prisms, which provides optimal redirection of light from the light source of a backlight device to the observer. This configuration may also allow improved brightness and evenness of the LCD luminance by directing the light of the backlight device, mainly, in a normal (perpendicular) direction to the display surface.
The set of prisms, which have a three-angled and more complicated cross-section, or square pyramids in modified form of the cross-section, are used in displays as optical antireflection films according to the JP Pat. No 9,005,505 [2], for example. Such constructions are often used as optical antireflection films, and the main problem discussed in [2] is to narrow the directional diagram along specified direction. The principal feature of such optical antireflection films is that a refraction coefficient of pyramids and prisms in such films is more than the refraction coefficient of the material covering them, which is necessary for a full inside reflection of light.
The use of pyramids and cone shells on the optical antireflection films prism surface for improving the directional diagram of radiation along a specified direction is also described in U.S. Pat. No. 5,467,417 [3].
U.S. Pat. No. 2,022,639 [4], includes the set of pyramids made of an optically transparent material, which changes the direction of light passing through the film. Such reflector reflects the light which falls on it along several predetermined directions. The predetermined directions number depends on the number of planes of the pyramids.
The drawback of the above described configurations consists of the insufficient reflective power of one side of a film and insufficient pass-through power of the other side of the film.
The present invention is directed to an optical film which offers better reflection of light falling from one side, and better pass-through of light falling from the other side.